Modeling the sensitivity dependence of silicon-photonics-based ultrasound detectors

source: © 2017 Optical Society of America

With recent advances in optical technology, interferometric sensing has grown into a highly versatile approach for ultrasound detection, with many interferometric detectors relying on optical waveguides to achieve high levels of sensitivity and miniaturization. In this Letter, we establish a practical model for assessing the sensitivity of silicon-photonics waveguides to acoustic waves. The analysis is performed for different polarizations, waveguide dimensions, and acoustic wave types. Our model was validated experimentally in the acoustic frequency band of 1–13 MHz by measuring the sensitivities of the two polarization modes in a silicon strip waveguide. Both the experimental results and theoretical prediction show that the transverse-magnetic polarization achieves a higher sensitivity and suppression of surface acoustic waves compared to the transverse-electric polarization for the geometries studied. [Read More…]

Fig. 2. Numerical calculation of normalized sensitivity ?? as a function of the waveguide width (??) and height (??) and polarization for (a), (b) the longitudinal acoustic wave in normal incidence and (c), (d) SAWs created in oblique incidence.

Shai Tsesses, Daniel Aronovich, Assaf Grinberg, Evgeny Hahamovich, and Amir Rosenthal “Modeling the sensitivity dependence of silicon-photonics-based ultrasound detectors”, Optics Letters Vol. 42, Issue 24pp. 5262-5265 (2017)

Analysis of Negatively Focused Ultrasound Detectors in Optoacoustic Tomography

A schematic description of acoustic absorbers in increasing sizes and a quantitative demonstration of the low-pass effect caused by the convex acoustic detector.

source:© 2017 IEEE Transactions on Medical Imaging

In optoacoustic tomography, negatively focused transducers may be used for improving the tangential image resolution while preserving a high signal-to-noise ratio. Commonly, image reconstruction in such scenarios is facilitated by the use of the virtual-detector approach. Although the validity of this approach has been experimentally verified, it is based on an approximation whose effect on optoacoustic image reconstruction has not yet been studied. In this paper, we analyze the response of negatively focused acoustic detectors in 2D in both time and frequency domains. Based on this analysis, tradeoffs between the detector size, curvature, and sensitivity are formulated. In addition, our analysis reveals the geometrical underpinning of the virtual-detector approximation and quantifies its deviation from the exact solution. The error involved in the virtual-detector approximation is studied in image reconstruction simulations and its effect on image quality is shown. The theoretical tools developed in this work may be used in the design of new optoacoustic detection geometries as well as for improved image reconstruction.
[Read More…]

Schematic illustration of (a,b) tangential and (c,d) non-tangential impact between of an impinging acoustic wave on a convex detector. (a,c) An illustration of the intersection of the acoustic wavefront with the detector surface and (b,d) of the corresponding phase factor exp[ikL(θ)] . The figure illustrates the conclusion from the SPM analysis given in (16) and (17): In the case of tangential intersection L∼θ2 and the integration over exp[ikL(θ)] in (15) is not cancelled out, whereas in the case on non-tangential intersection L∼θ which causes nullification of exp[ikL(θ)] under integration.

G. Drozdov and A. Rosenthal “Analysis of Negatively Focused Ultrasound Detectors in Optoacoustic Tomography,” accepted to Transactions on Medical Imaging ( Volume: 36 , Issue: 1 , Jan. 2017 )

Fiber interferometer for hybrid optical and optoacoustic intravital microscopy

source: © 2017 Optical Society of America

The addition of optoacoustic sensing to optical microscopy may supplement fluorescence contrast with label-free measurements of optical absorption, enhancing biological observation. However, the physical dimensions of many optoacoustic systems have restricted the implementation of hybrid optical and optoacoustic (O2A) microscopy to imaging thin samples in transmission mode or to ex-vivo investigations. Here we describe a miniaturized optoacoustic sensor, based on a ?-phase-shifted fiber Bragg grating embedded in an acoustic cavity, which is virtually invisible to the optical path and can be seamlessly integrated into any conventional optical microscope. The new sensor enables, for the first time to our knowledge, entirely optical O2A intravital microscopy in epi-illumination mode, demonstrated by label-free optoacoustic and second-harmonic generation images of a mouse abdomen and ear. Our technique greatly simplifies the integration of acoustic detection in standard microscopes and could therefore make optoacoustic microscopy more accessible to the biomedical community. [Read More…]

Fig. 5. Schematic depiction of the O2A microscopy setup: A standard inverted microscope with laser sources for optoacoustic and non-linear optical imaging is combined with galvanometric mirrors for fast laser raster scanning. The sensor is mounted on the microscope objective, with a tunable CW laser coupled to the embedded ?-FBG. The inset shows the 3D printed platform supporting an anesthetized mouse and mounted on a ??? positioning stage. DM, dichroic mirror; BP, bandpass filter; PH, pinhole; ND, neutral density filter; BS, beam splitter; PMT, photomultiplier tube; OA, optoacoustic; DAQ, data acquisition card.

Authors: Rami Shnaiderman, Georg Wissmeyer, Markus Seeger, Dominik Soliman, Hector Estrada, Daniel Razansky, Amir Rosenthal, and Vasilis Ntziachristos, “Fiber interferometer for hybrid optical and optoacoustic intravital microscopy,” Optica 4, 1180-1187 (2017)